Invited Paper SS2-ThA6
Dynamics of Electron Transfer and Exciton Formation at Interfaces
Thursday, October 31, 2013, 3:40 pm, Room 202 A
We have studied the ultrafast dynamics of photoinduced electron transfer and solvation processes at the water ice-metal interface and focus here on the effect of co-adsorbed alkali ions (Na, K, Cs). Femtosecond time-resolved two-photon-photoemission (2PPE) spectroscopy provides direct access to elementary processes like electron injection and the subsequent solvation dynamics which competes with the electron transfer back to the Cu(111) substrate. In particular, we study the electronic structure changes and ultrafast dynamics for the bulid-up of a solvation shell (up to 6 water molecules) around individual alkali atoms at the metal surface and compare with electronic structure calculations. For ice mulitlayers doped with alkali ions we observe the formation of longlived electron alkali-water complexes.As an example for a hybrid system of inorganic and organic semiconductors we investigate the electronic structure and dynamics at the ZnO(10-10) surface and the influence of hydrogen and pyridine adsorption. Hydrogen termination leads to the formation a metallic surface band, whereas pyridine adsorption results in a quite substantial work function reduction (up to 2.9 eV), which may be useful for controlling the energy level alignment at inorganic/organic interfaces. Furthermore we directly monitor the ultrafast relaxation of hot photocarriers in the ZnO conduction band and the subsequenst formation of an excitonic state at the ZNO surface on ps timescales.